Arena construction

We are looking at constructing an arena on sort of level gravley/sandy terrain. We have no idea where to start, so we will be looking for someone to come and do the base, minimal leveling, drainage, and fill. We are expecting it to be quite costly, but from anyone who has experince recently with the construction of an arena similar to my situation:
- How much did yours cost
- What is the best fill for Extreme weather (really hot to really wet)
- Also the best fill for multi purpose use (dressage and showjumping)
-what company did you use?

We are well aware that the arena will not be cheap but we would still like to keep costs at a mini